For example, in a nuclear power plant including a Pressurized Water Reactor (PWR), light water is used as a nuclear reactor coolant and a neutron moderator and becomes high-temperature and high-pressure water that do not boil surrounding the entire reactor core, the high-temperature and high-pressure water is fed to a steam generator, steam is generated by heat exchange, and the steam is fed to a turbine generator to generate electricity.
In the nuclear power plant, it is necessary to examine various structures or the like of the pressurized water reactor at fixed intervals in order to secure sufficient safety and reliability. In addition, when the examination is performed and defects are found, necessary locations related to the defects are repaired. For example, in the pressurized water reactor, a plurality of instrumentation tube supports penetrating a lower head are provided in a reactor vessel main body, and in each instrumentation tube support, a conduit tube is connected to the lower end portion outside the reactor while an in-core instrumentation guide tube is fixed to the upper end portion inside the reactor. In addition, a neutron flux detector capable of measuring a neutron flux is inserted from the instrumentation tube support into a reactor core (fuel assembly) through the in-core instrumentation guide tube by the conduit tube.
An in-core instrumentation tube is fitted so as to be welded to a mounting hole of the reactor vessel main body, and thus, the instrumentation tube support is configured. Accordingly, tensile stress may remain on the in-core instrumentation tube, or the welded section of the in-core instrumentation tube and the periphery of the welded section, and thus, probability of occurrence of stress corrosion cracking due to long-time use becomes higher. Therefore, in the related art, there is a technology of water jet peening that prevents the stress corrosion cracking by improving tensile residual stress of a surface so as to be compression residual stress. In the water jet peening, high-pressure water including cavitation bubbles is sprayed on the surface of a metal member in water, and the tensile residual stress on the surface of the metal member is improved so as to be the compression residual stress. For example, this water jet peening device is disclosed in PTL 1 below.
In the water jet peening device disclosed in PTL 1, a spray nozzle is configured to swivel centered on an instrumentation tube support, to be raised and lowered in a vertical direction (up-down direction) of the instrumentation tube support, to swing in the downward direction or a direction inclined with respect to the instrumentation tube support, and to move in a front-rear direction in which the spray nozzle approaches or moves away from the instrumentation tube support. Accordingly, the water jet peening is performed on the outer circumferential surface of the instrumentation tube support, and the welded section of the instrumentation tube support with respect to the reactor vessel.